임베디드시스템기초 (# ) #11. Serial Communications 한림대학교전자공학과이선우

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1 임베디드시스템기초 (# ) #11. Serial Communications 한림대학교전자공학과이선우

2 Contents General Serial communications Asynchronous serial communications (UART) 2

3 Parallel vs. Serial 패러럴 ( 병렬 ) 데이터통신 복수의신호선을이용 ( 대개 8/16/32bit) 올바른데이터교환을위해일정한순서-이를프로토콜, 대개 Handshake방식-로진행 Ex) up와외부메모리와의데이터통신방식, PC의패러랠포트 (8bit) 시리얼 ( 직렬 ) 데이터통신 (Serial communication) 하나의신호선을이용따라서일정한시간간격 ( 이를 baudrate) 으로데이터를교환 Ex) PC 시리얼포트 (COM port), 대개의 MCU의주외부와의통신방법으로이용 Ref.: 3

4 Parallel vs. Serial Communication channel or Computer bus Tx Signal Clock Rx Tx Signal D3 1 D2 0 D1 0 D0 0 Rx 4

5 Examples of serial communications Morse code telegraphy RS-232 (low-speed, implemented by serial ports) * RS-423 RS-485 I²C * Serial Peripheral Interface Bus (SPI) * Universal Serial Bus (moderate-speed, for connecting peripherals to computers) FireWire Ethernet Fibre Channel (high-speed, for connecting computers to mass storage devices) InfiniBand (very high speed, broadly comparable in scope to PCI) MIDI control of electronic musical instruments DMX512 control of theatrical lighting SDI-12 industrial sensor protocol Serial Attached SCSI Serial ATA 5

6 Asynchronous vs. Synchronous Asynchronous ( 비동기 ) 통신 송신자와수신자가전송이전에동기화필요없음. 동기를위한별도신호필요없음. 대신송 / 수신자는반드시동일한클럭주파수를알아야하고, 내장된동기신호 (start/stop bit 등 ) 존재해야함항상전송할정보를갖지않는장치, 예로키보드, 마우스등에적합대표적인표준안 : RS-232C, USB 등 Synchronous ( 동기 ) 통신 비동기와같이데이터전송선이외에별도의동기를위한신호선 ( 클럭 signal) 필요주요장점 : 수신자가여러클럭속도에대응가능표준안 : I 2 C ( 필립스 ), SPI(Motorola) 등 6

7 UART: PC side standard (RS-232C) RS-232C 란? EIA (Electronics Industry Association) 표준안단체에서시리얼통신을위해정한전기적표준안이름 A "Space" (logic 0) will be between +3 and +25 Volts. A "Mark" (Logic 1) will be between -3 and -25 Volts. The region between +3 and -3 volts is undefined. An open circuit voltage should never exceed 25 volts. (In Reference to GND) A short circuit current should not exceed 500mA. 표준안에의해 8m 정도까지는보장해야함 ( 실제 RS-232C를사용해서 100m 정도까지가능 ) 18개의다른신호선들정의 : GNC, RXD, TXD, DCD, DTR, CTS, RTS, etc EIA-232D (1987), EIA-232E(1991) 등으로발전됨 * 7

8 Waveform Logical Physical voltage level ASCII K (0x4b) 8

9 Level converter 대개의 MCU 시스템이나디지털시스템은 TTL/CMOS logic level(0,5/3.3v) 로구동되나, RS-232 신호는 12V 범위에서구동되므로전압의변환이필요. 이러한일을담당해주는 chip 들 - 일종의 dc-dc converter- 이개발, 판매되고있음. 가장대표적인칩이 MAXIM 의 MAX-232/233 임. 9

10 대표적인시리얼통신용프로그램 MS Windows OS 의하이퍼터미널 프로그램 보조프로그램 통신 하이퍼터미널 설정방법 Parity bit 전송상의에러를찾기위한방법 2 종류 : even( 짝수 ), odd( 홀 ) parity 패리티비트까지포함하여 1 의개수가짝 / 홀수가되도록결정함. ex. Data 이라면 - Even parity bit=0 - Odd parity bit=1 10

11 Flow control (Handshaking) Software flow control: ASCII XON (17d,11h) & XOFF (19d,13h) code 를이용하여제어 대개버퍼의수가아주적은모뎀과통신시이용 예 : 모뎀버퍼가다차면모뎀은컴퓨터로 XOFF code 전송하여잠시중단시키고, 이후여유가생기면 XON code 전송하여재전송이루어짐. 장점 : 별도의신호선필요없으나속도저하됨 Hardware flow control: 별도의신호선 (RTS/CTS) 이용 컴퓨터가신호를보내기전에 RTS 활성화시키고, 모뎀이수신가능하면 CTS 를활성화시킴. 11

12 MSP430 에서의통신모듈 Universal serial communication interface (USCI) module The USCI_Ax modules support: UART mode Pulse shaping for IrDA communications Automatic baud rate detection for LIN communications SPI mode The USCI_Bx modules support: I 2 C mode SPI mode The universal synchronous/asynchronous receive/transmit (USART) module SPI mode UART mode FG461X series has - USCI_A0 module: SPI (3 or 4 pin), UART, enhanced UART and IrDA. -USCI_B0 : SPI (3 or 4 pin) and I2C. - USART1 : UART (double buffered), SPI 12

13 USCI: UART mode (ch.19) USCI_Ax modules Use 2 pins: UCAxRXD, UCAxTXD Features 7- or 8-bit data with odd, even, or non-parity Independent transmit and receive shift registers Separate transmit and receive buffer registers LSB-first or MSB-first data transmit and receive Built-in idle-line and address-bit communication protocols for multiprocessor systems Receiver start-edge detection for auto-wake up from LPMx modes Programmable baud rate with modulation for fractional baud rate support Status flags for error detection and suppression Status flags for address detection Independent interrupt capability for receive and transmit 13

14 USCI initialize USCI 모듈의초기화 / 재설정순서 UCSWRST( SW reset flag in UCAxCTL1)=1 관련 reg. 들설정 포트설정 UCSWRST=0 수신 / 송신 enable ( 즉 module ON) Enable interrupts (UCAxRXIE, UCAxTXIE) Character format 14

15 Automatic Error detection Receive error condition 15

16 Baud rate generator UART 통신을위해선정해진통신속도 ( 이를 bit rate or baud rate 이라함 ) 를준수해야함. 이를위한클럭발생기를 BR generator 라함. 크게 2 개모드로동작 Low-frequency mode: UCOS16=0, low-freq. clock source 이용, 저전력가능. 높은 bps 에서오차큼. Oversampling mode: UCOS16=1 관련 reg.: Baud rate control reg.: UCAxBR0, UCAxBR1 Modulation control reg.: UCAxMCTL Table 19-4, 19-5 의설정값이용 16

17 USCI Interrupts TX/RX 각각하나씩의인터럽트가존재 : UCAxTXIFG, UCAxRXIFG Transmit 송신완료후새로운데이터를받을준비가되면 ( 즉 UCAxTXBUF empty) TXIFG=1이됨. 새로운데이터를 TXBUF에쓰면자동적으로 reset Receive 1 frame data를수신하고이를 RXBUF에넣은후발생 RXBUF를읽으면자동으로 RXIFG reset USCI_Ax/USCI_Bx 가인터럽트벡터공유 SW 에서어떤모듈이 IRQ 발생했는지구별해야함. 17

18 Example code for USCI-UART operation void main(void) { volatile unsigned int i; WDTCTL = WDTPW+WDTHOLD; // Stop WDT P4SEL = 0x0C0; // P4.7,6 = USCI_A0 RXD/TXD UCA0CTL1 = UCSSEL_2; // SMCLK UCA0BR0 = 0x09; // 1MHz UCA0BR1 = 0x00; // 1MHz UCA0MCTL = 0x02; // Modulation UCA0CTL1 &= ~UCSWRST; // Initialize USCI state IE2 = UCA0RXIE; // Enable USCI_A0 RX interrupt } low_power_mode_0(); // Echo back RXed character, confirm TX buffer is ready first #pragma vector=usciab0rx_vector interrupt void USCIA0RX_ISR (void) { while(!(ifg2&uca0txifg)); UCA0TXBUF = UCA0RXBUF; // TX -> RXed character } 18